Voltage generator circuit

ABSTRACT

Embodiments are provided that include a circuit for generating voltage in a memory. One such circuit includes a charge pump circuit including a first transistor, a high-voltage switch circuit, and a cut-off switch circuit arranged to reduce leakage current from the charge pump circuit. The cut-off switch circuit includes a second transistor, wherein an output of the charge pump circuit is coupled to one of a source node and a drain node of the second transistor, and a first control signal is input at a gate of the second transistor. Further embodiments provide a method for generating voltage. One such method includes enabling a first transistor coupled to an output of a charge pump circuit when the charge pump is operating and disabling the first transistor coupled to the output of the charge pump circuit when the charge pump circuit is not operating.

BACKGROUND

1. Field of the Invention

Embodiments of the invention relate generally to the field of memorydevices and more particularly, to reducing leakage currents anddischarging power in a voltage generator circuit of a memory device.

2. Description of the Related Art

Flash memory is a non-volatile memory that can be electrically erasedand reprogrammed. It is primarily used in memory cards, USB flashdrives, and the like for storage of data in computer systems. Generally,flash memory stores information on an array of floating gatetransistors, called “cells”, each of which traditionally stores one bitof information. Each cell is characterized by a threshold voltage (Vt).By adding or removing charge from a floating gate, the threshold voltageof the cell changes, thereby defining whether the cell is programmed orerased. The threshold voltage level indicates the value for a single bitof information, generally represented as a 1 or 0. Multi-level cells mayinclude more than two ranges that are representative of additionalvalues, such as two or more bits of information. In memory cells, thevoltages supplied include program verify voltages, read voltages, erasevoltages, and the like. A memory device generally includes one or morevoltage sources that provide these and other voltages to the cells ofthe memory array and/or to other locations within the memory device. Incertain configurations, the supplied voltages are provided by internalvoltage generators that are connected to transistors that make up thecells. For instance, each memory device can include multiple voltagegenerators that are configured to output a voltage for the program, readand verify operations.

To generate high voltages (e.g., voltages above a common voltage (Vcc)),such as program and erase voltages, the voltage generators often employa charge pump circuit that is capable of supplying the desired voltagelevels. The high voltage power output from the charge pump circuit istransferred to other locations in the flash memory via high-voltageswitching circuits (HV switching circuits). Unfortunately, duringperiods when the charge pump circuit is not operating, the stand-bycurrent of the charge pump circuit may leak to a lower-potential node.This may be referred to as a leakage current. For example, a leakagecurrent can flow from the charge pump circuit through the HV switchingcircuit. Further, when the charge pump circuit is not operating, it maybe desirable that charges remaining at nodes within the voltagegenerator be discharged. Discharging may avoid overstressing a cell witha voltage that could otherwise remain on the output lines.

Embodiments of the present invention may be directed to one or more ofthe problems set forth above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a voltage generator in accordancewith one or more embodiments of the present invention;

FIG. 2 is a schematic diagram illustrating a charge pump circuit of thevoltage generator in accordance with one or more embodiments of thepresent invention;

FIG. 3 is a schematic diagram illustrating a high-voltage switchingcircuit of the voltage generator in accordance with one or moreembodiments of the present invention;

FIG. 4 is a block diagram illustrating a voltage generator including acut-off switch circuit in accordance with one or more embodiments of thepresent invention;

FIG. 5 is a block diagram illustrating a voltage generator including adischarge circuit in accordance with one or more embodiments of thepresent invention;

FIG. 6 is a schematic diagram illustrating a discharge circuit inaccordance with one or more embodiments of the present invention;

FIGS. 7A and 7B are timing diagrams of control signals in accordancewith one or more embodiments of the present invention;

FIG. 8 is a schematic diagram illustrating a discharge circuit inaccordance with one or more alternate embodiments of the presentinvention;

FIG. 9 is a schematic diagram illustrating a voltage generator includinga plurality of discharge circuits in accordance with one or moreembodiments of the present invention;

FIG. 10 is a schematic diagram illustrating a voltage generatorincluding a plurality of discharge circuits in accordance with one ormore alternate embodiments of the present invention;

FIG. 11 is a block diagram illustrating a voltage generator including acut-off switch circuit in accordance with one or more embodiments of thepresent invention;

FIG. 12 illustrates a block diagram of a processor-based device having amemory that includes memory devices in accordance with one or moreembodiments of the present invention;

FIG. 13 illustrates a block diagram of a memory device having a memoryarray in accordance with one or more embodiments of the presentinvention; and

FIG. 14 is schematic diagram of a NAND flash memory array having memorycells in accordance with one or more embodiments of the presentinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

FIG. 1 includes a block diagram that depicts a voltage generator, asgenerally designated by reference numeral 10. The voltage generator 10includes a charge pump circuit 12 and a switch circuit 14. The chargepump 12 includes a high-voltage output (Vpp) that is coupled to theswitch circuit 14 via a path 16, and the switch circuit 14 includes anoutput voltage (Vout) on a path 18. High-voltage may be defined as avoltage level that is above the level of a common voltage (Vcc) of thesystem. For example, one embodiment, the program, verify and/or erasevoltages may be above the common voltage (Vcc) (i.e., high-voltage).Accordingly, a high-voltage charge pump circuit may include a firsttransistor, an input at a supply voltage and an output voltage that ishigher than the supply voltage, for instance. The path 18 from theswitch circuit 14 may be electrically coupled to various locations in amemory device, such as the transistors of memory cells, or other powerconsuming devices. Accordingly, the high-voltage output (Vpp) of thecharge pump 12 can be routed via the switch circuit 14 to variouslocations in the memory device. Similar to a high-voltage charge pumpcircuit, a high-voltage switch circuit may include an output that ishigher than the common voltage (Vcc).

FIG. 2 illustrates an embodiment of the charge pump circuit 12. Thecharge pump circuit 12 includes a common-collector voltage (Vcc) that isprovided to the charge pump circuit 12 via an input node 20. Further,the charge pump circuit 12 includes a plurality of transistors 22. Inone embodiment, the transistors 22 include low-threshold voltage (Vt)high-voltage nmosfets (HV nmosfets). The low Vt HV nmosfets can operatewith a low Vcc (e.g., Vt having a value of about 0.2V and Vcc having avalue of about 3V). The charge pump circuit 12 also includes a pluralityof capacitors 24. The capacitors 24 are capable of storing power havinga higher voltage than Vcc. For instance, in operation, the transistors22 are implemented as switches that are enabled and disabledcooperatively to charge the capacitors 24. The high-voltage output (Vpp)of the charge pump circuit 12 is output via the path 16, as discussedpreviously with regard to FIG. 1.

FIG. 3 illustrates an embodiment of the switch circuit 14. The switchcircuit 14 includes a high-voltage switch circuit. Power at the Vcclevel is provided to the switch circuit 14 via three inputs 26, 28 and30. An input of the switch circuit 14 includes Vpp that is routed to theswitch circuit 14 via the path 16. The path 16 carries Vpp from thecharge pump circuit 12 to the switch circuit 14. As is discussed belowwith regard to FIGS. 4-9, the path 16 may also route other voltagelevels (e.g., Vppo) into the switch circuit 14. The switch circuit 14also includes a plurality of transistors 32. In one embodiment, thetransistors 32 may be low Vt nmosfets. The switch circuit also includesa transistor 34 coupled to the path 18 of Vout. In one embodiment, thetransistor 34 includes a normal-threshold voltage high-voltage nmosfet(Vt HV nmosfet). The output voltage (Vout) of the switch circuit 14 isoutput via the path 18, as discussed previously with regard to FIG. 1.

In operation of the voltage generator 10, the charge pump circuit 12receives the incoming power (Vcc) and incrementally stores the power inthe capacitors, in turn storing power with a voltage level that ishigher than Vcc. The charge pump circuit 12 discharges the high-voltageoutput (Vpp) across the path 16. The switch circuit 14 receives thepower (Vpp) and routes the output power (Vout) to various locationswithin a memory device. For instance, the switch circuit 14 may beembedded in a row decoder that routes the output power (Vout) to a gateof a memory cell transistor. Unfortunately, when the switch circuit 14is disabled (e.g., closed), a leakage current may still exist across theswitch circuit 14, draining current from the charge pump circuit 12.

FIG. 4 illustrates an embodiment of the voltage generator 10 thatincludes an additional cut-off switch circuit 36. The cut-off switchcircuit 36 can be configured to reduce or possibly eliminate the leakagecurrent. In the illustrated embodiment, the cut-off switch circuit 36 isdisposed in the path 16, between the charge pump circuit 12 and theswitch circuit 14. The path 16 is split into a path 16 a carrying thehigh voltage (Vpp) from the charge pump circuit 12 to the cutoffswitching circuit 36, and a path 16 b routing a high voltage (Vppo)output of the cut-off switch circuit 36 to the switch circuit 14.

In the illustrated embodiment, the cut-off switch circuit 36 includes atransistor 38. The transistor 38 includes a standard-threshold voltagehigh-voltage pmosfet. A pmosfet having a large channel width may have asmall voltage drop across the transistor 38. Accordingly, the level ofthe high voltage (Vppo) on the path 16 b may be equal to or less thanthe high voltage (Vpp) at the path 16 a.

The output of the charge pump circuit 12 is coupled to a node (e.g., asource node) of the transistor 38, and a control signal (disable1) isinput to a control gate of the transistor 38. The switch circuit 14 iscoupled to a node (e.g., a drain node) of the transistor 38.Accordingly, based on the level of the control signal (disable1), thetransistor 38 can limit the current that passes from the charge pumpcircuit 12 to the switch circuit 14.

For example, when the control signal (disable1) is in a logic-highstate, the transistor 38 is disabled, blocking current from beingconducted across the transistor 38, and reducing the potential that aleakage current exists across the switch circuit 14. The logic-highstate of the control signal (disable1) can include various voltagelevels that are dependent on the threshold voltage level of thetransistor 38. In one embodiment, the logic-high state of the controlsignal (disable1) includes Vcc. In other words, the voltage level of thelogic-high of the control signal (disable1) is the same as the supplyvoltage level of the charge pump circuit 12.

When the control signal (disable1) is in a logic-low state, thetransistor 38 is enabled, and current can be conducted across thetransistor 38 to the switch circuit 14. The logic-low state of thecontrol signal (disable1) can include various voltage levels that aredependent on the threshold voltage level of the transistor 38. In oneembodiment, the logic-low state of the control signal (disable1)includes about zero volts (V).

In operation of the voltage generator 10, the state/voltage level of thecontrol signal (disable1) input to the gate of the transistor 38 isvaried based on the operation of the charge pump circuit 12. Forexample, when the charge pump circuit 12 is not operating (e.g., notconfigured to generate the high voltage output (Vpp) on the path 16),the transistor 38 is disabled, and when the charge pump circuit 12 isoperating (e.g., configured to generate the high voltage output (Vpp) onthe path 16), the transistor 38 is enabled. In other words, the controlsignal (disable1) is maintained in a logic-high state when the chargepump circuit 12 is not operating and is maintained in a logic-low statewhen the charge pump circuit 12 is operating. The logic-high state caninclude a voltage level of Vcc, as discussed previously, and thelogic-low state can include a voltage below Vcc, such as at or near 0V.Accordingly, when the charge pump circuit 12 is not operating, a Vcclevel control signal disables the transistor 38 to reduce the leakagecurrent across the switch circuit 14, and when the charge pump circuit12 is operating, a 0V level control signal enables the transistor 38such that a current can flow across from the charge pump circuit 12,across the transistor 38, and be routed via the switch circuit 14.

After the charge pump circuit 12 operates, and is no longer operating, acharge may remain in the voltage generator 10. For example, after thecharge pump circuit 12 operates and the transistor 38 is disabled, acharge may remain in the charge pump circuit 12, the switch circuit 14,the path 16 between them, and the output path 18 of the switch circuit14. The high voltage level (Vppo) may be floating. If the chargeremains, a portion of the memory device coupled to the output path 18 ofthe switch circuit 14 (e.g., a gate of a memory cell) may continue to beexposed to the voltage due to the remaining charge. The charge may bedischarged to avoid overstressing a memory cell with the voltage.

FIG. 5 illustrates an embodiment of the voltage generator 10 including adischarge circuit 40 coupled to a node 42 on the path 16 b between thetransistor 38 and the switch circuit 14. A control signal (disable2) isrouted into the discharge circuit 40. The discharge circuit 40 isemployed to discharge charges in the voltage generator 10 to a lowerpotential during a period when the charge pump circuit 12 is notoperating.

FIG. 6 illustrates an embodiment of the discharge circuit 40. Thedischarge circuit 40 includes a transistor 44. In the illustratedembodiment, the transistor 44 includes an nmosfet device. A drain nodeof the transistor 44 is coupled to the node 42 between the cut-offswitch circuit 36 and the switch circuit 14, and is, in turn, coupled tothe drain node of the transistor 38 of the cut-off switching circuit 36.A source node 46 of the transistor 44 is coupled to a lower-potentialnode 46, having a lower potential than the node 42 between the cut-offswitch circuit 36 and the switch circuit 14. In one embodiment, thelower-potential node 46 is coupled to ground. The control signal(disable2) is coupled to a gate of the transistor 44.

When the voltage level of the control signal (disable2) is high enough,the gate bias (Vg) is greater than the threshold voltage (Vt) of thetransistor 44, and within the transistor 44 an inversion layer is formedthat enables the flow of electrons (e.g., current). In other words, thetransistor 44 is enabled, and current can be conducted from the drain(node 42) to the source (node 46) of the transistor 44. In theillustrated embodiment, where the control signal (disable2) islogic-high and is greater than the threshold voltage (Vt), thetransistor 44 of the discharge circuit 40 is enabled, and charges at thenode 42 between the cut-off switch circuit 36 and the switch circuit 14are discharged.

When the voltage level of the control signal (disable2) is too low, thegate bias (Vg) is less than the threshold voltage (Vt) of the transistor44, and an inversion layer is not formed across the transistor 44. Inother words, the transistor 44 is disabled, and current is blocked fromflowing from the drain (node 42) to the source (node 46) of thetransistor 44. In the illustrated embodiment, where the control signal(disable2) is logic-low and is less than the threshold voltage (Vt), thetransistor 44 of the discharge circuit 40 is disabled, and the charge atthe node 42 between the cut-off switch circuit 36 and the switch circuit14 is not discharged.

Even when the control signal (disable1) is in a logic-low state, thehigh voltage level (Vpp) and the voltage of the internal nodes of the ofcharge pump circuit 12 do not fall below the absolute value of thethreshold voltage (Vt) of the transistor 38. The voltage generator 10can eliminate a large peak current, and a large stand-by current withoutmuch, if any, overhead in area or complexity.

The level of the control signals (disable1 and disable2) can be variedbased on the application. For example, the control signals (disable1 anddisable2) may include logic-high and or logic-low states that are aboveVcc, below Vcc, the same as Vcc, or any combination thereof. Further,the control signals (disable1 and disable2) can have logic levels thatare different from one another or that are the same. In one embodiment,the control signal input into the transistor 38 (disable1) and thecontrol signal (disable2) input to the gate of the transistor 44 havethe same logic-high and logic-low voltage levels. For example, thelogic-high level of the control signals is Vcc and/or the logic-lowlevel is approximately 0V. Further, in one embodiment, the controlsignals (disable1 and disable2) are the same signal that is input to thegates of both of the transistors 38 and 44. In other words the controlsignals (disable1 and disable2) have approximately the same profile, andmay be received from the same source or a different source.

FIG. 7A illustrates a timing diagram of an embodiment where the controlsignals (disable1 and disable2) are the same. For example, in a firstregion 48, the control signals (disable1 and disable2) are both in alogic-high state, in a second region 50 the control signals (disable1and disable2) are both in a logic-low state, and in a third region 52the control signals (disable1 and disable2) are both in logic-highstate. In one embodiment, the first region 48 and the third region 52include a period where the charge pump circuit 12 is not operating, andthe second region 50 includes a period where the charge pump circuit 12is operating. Accordingly, in the first region 48 and third region 52,the transistor 38 is disabled by the logic-high control signal(disable1) to block the leakage current, and the transistor 44 isenabled by the logic-high control signal (disable 2) to discharge theremaining charge. In the second region 50, the transistor 38 is enabledby the logic-low control signal (disable1) to enable current to flow tothe switch circuit 14, and the transistor 44 is disabled by thelogic-low control signal (disable 2) to block current from dischargingto the lower-potential node 46.

FIG. 7B illustrates a timing diagram for an alternate embodiment of thecontrol signals (disable1 and disable2). The control signals (disable1and disable2) include a delay between their transition states such thatlogic of the control signal (disable1) changes from a high to low stateafter the control signal (disable2) changes from the high to low state,and the control signal (disable1) changes from the low to the high stateprior to the control signal (disable2) changing from the low to highstate. For example, a first delay region 54 includes a delay between thetransition of the control signals (disable1 and disable2) from thelogic-high state to the logic-low state, and a second delay region 56includes a delay between the of the transition of the control signals(disable1 and disable2) from the logic-low state to the logic-highstate. The delay between the transition of the control signals (disable1and disable2) may prevent a direct path (e.g. short) between the chargepump circuit 12 and the lower-potential node 46. In other words, thedelay may help to ensure that the transistor 38 is enabled only when thetransistor 44 is disabled. Where the threshold voltage (Vt) of thetransistor 38 is not high (e.g., less than Vcc), the timing diagram ofFIG. 7B may reduce the likelihood of the high voltage level (Vpp) fromreducing to or below a level that is the sum of Vcc and the absolutevalue of the voltage threshold of the transistor 38.

FIG. 8 illustrates an alternate embodiment of the discharge circuit 40.The discharge circuit 40 of FIG. 8 includes a first transistor 60 and asecond transistor 62. In the illustrated embodiment, the firsttransistor 60 includes depletion-type nmosfet device, and the secondtransistor 62 includes an enhancement-type pmosfet device.

A drain node of the first transistor 60 is coupled to the node 42between the cut-off switch circuit 36 and the switch circuit 14, and is,in turn, coupled to the drain node of the transistor 38 of the cut-offswitch circuit 36. A source node 64 of the first transistor 60 iscoupled to a source node of the second transistor 62. A drain of thesecond transistor 62 is coupled to the lower-potential node 46. In oneembodiment, the lower-potential node 46 is coupled to ground.

The control signal (disable2) is coupled a gate of the first transistor60 via a direct path 65. The control signal (disable2) is coupled to agate of the second transistor via a second path 66. The second path 66includes an inverter 67 between the input of the control signal(disable2) and the gate of the second transistor 62. Accordingly, thecontrol signal (disable2) at the gate of the second transistor 62includes a logic level that is the inverse of the control signal(disable2) at the gate of the first transistor 60.

During a period while the voltage (Vppo) at the node 42 is charged tothe high voltage level (Vpp), the control signal (disable2) is set at alogic-low state. During this period, the voltage at the source node ofthe first transistor 60 reaches the level of the absolute value of thethreshold voltage of the first transistor 60. When the sum of theabsolute value of the threshold voltage of the second transistor 62 andthe voltage level of Vcc is greater than the absolute value of thethreshold voltage of the first transistor 60, the discharging circuit 40is cut-off such that current does not flow across the dischargingcircuit 40 to the lower-potential node 46.

After the charge pump circuit 12 is disabled, the discharge operationbegins. The control signal (disable2) is driven to a logic-high level.Early in the discharge operation, the voltage at the source node of thefirst transistor 62 is the sum of Vcc and the absolute value of thethreshold voltage of the first transistor 60. When the sum of Vcc andthe absolute value of the threshold voltage of the first transistor 60is greater than the absolute value of the threshold voltage of thesecond transistor 62, the second transistor 62 is enabled and charges atthe node 42 (e.g., Vppo) are discharged. When the voltage level (Vppo)at the node 42 reaches the absolute value of the threshold voltage ofthe second transistor 62, the discharging operation is automaticallystopped.

When Vcc is about 3V, the threshold value of the first transistor 60 andthe second transistor 62 may be set to about −3V. Accordingly, after thedischarging operation, the output voltage (Vout) at the path 18 mayremain at a voltage level approximately equivalent to Vcc. Otherembodiments may include other settings (e.g. threshold voltages andlevels for Vcc).

Where the threshold voltage of the first transistor 60 is higher thanVcc, the lower-potential node 46 may be coupled to Vcc. In such aconfiguration, the charges from the output voltage (Vout) at the path 18return to Vcc and can be recycled. This is possible because no forwardbias regime occurs while the discharger circuit 40 is disabled, and thisis because the source voltage of the second transistor 62 (the absolutevalue of the threshold voltage of the first transistor 60) is higherthan the drain voltage (Vcc).

FIG. 9 illustrates an embodiment of the voltage generator 10 includingdischarge circuits 40 coupled to internal nodes of the charge pumpcircuit 12. For example, in the illustrated embodiment, five dischargecircuits 40 are coupled to nodes of the charge pump circuit 12. Two ofthe discharge circuits 40 are coupled to nodes 70 proximate the gates ofthe transistors 22, two of the discharge circuits 40 are coupled tonodes 72 proximate capacitors 24, and one of the discharge circuits 40is coupled to a node 74 on the path 16 outputting the high voltage(Vpp). The control signal (disable2) is input in parallel to each of thedischarge circuits 40. Accordingly, the control signal (disable2) maysimultaneously control each of the discharge circuits 40 to dischargethe charge pump circuit 12 in a manner similar to that discussedpreviously with regard to FIGS. 5-8. Embodiments may include any numberof discharge circuits 40 coupled to any number of internal nodes of thecharge pump circuit 12.

The charge pump circuits 40 may include the charge pump circuitsdiscussed with regard to FIG. 6 and FIG. 8, or any combination thereof.FIG. 10 illustrates an embodiment of the voltage generator 10 employinga plurality of transistors coupled to one another in a similar fashionas the embodiments discussed with regard to FIG. 8. The voltagegenerator 10 and discharge circuit 40 include four of the firsttransistors 60 and one of the second transistor 62. In one embodiment,the first transistors 60 include a depletion-type nmosfet device, andthe second transistor 62 includes an enhancement-type pmosfet device.

The drain node of each of the first transistors 60 is coupled to atleast one internal node of the charge pump circuit 12. For example, twoof the first transistors 40 are coupled to nodes 70 proximate the gatesof the transistors 22, two of the first transistors 40 are coupled tonodes 72 proximate capacitors 24. The source node 64 of each of thefirst transistors 60 is coupled to the source node of the secondtransistor 62. Similar to the previously discussed embodiments, thedrain node of the second transistor 62 is coupled to a lower-potentialnode 46. In one embodiment, the lower-potential node 46 is coupled toground. In some embodiment, the lower-potential node 46 may be coupledto Vcc, or the like.

The control signal (disable2) is coupled in parallel to the gate of eachof the first transistors 60 via the path 65. The control signal(disable2) is coupled to the gate of the second transistor via thesecond path 66. The second path 66 includes the inverter 67 between theinput of the control signal (disable2) and the gate of the secondtransistor 62. Accordingly, the control signal at the gate of the secondtransistor 62 includes a logic level that is the inverse of the controlsignal (disable2) at the gate of the first transistor 60.

Similar to the embodiments discussed with regard to FIG. 8, thedischarge circuit 40 can be controlled via the control signal (disable2)to discharge the internal nodes of the charge pump circuit 12.Embodiments may include any number of discharge circuits 40 coupled toany number of internal nodes of the charge pump circuit 12.

Although the previous embodiments may include the transistor 38 of thecut-off switch circuit 36 having a given polarity, such as NPN typepolarity, additional embodiments of the voltage generator 10 may includethe transistor 38 having a different polarity, such as PNP typepolarity. These embodiments may also include variations in theconfigurations of the charge pump circuit 12 and the switch circuit 14.For example, FIG. 11 illustrates an embodiment of the voltage generator10 including the cut-off switch circuit 36 having a transistor 38 with apolarity (e.g., PNP) that is opposite from the polarity discussedpreviously (e.g., NPN). In such an embodiment, the charge pump circuit12 and the switch circuit 14 are disconnected from one another when thecontrol signal (disableb) of the cut-off switch 36 is in the disabled(low) state, and the charge pump circuit 12 and the switch circuit 14are connected to one another with the control signal (disableb) of thecut-off switch 36 in an enabled (high) state.

In the illustrated embodiment, the cut-off switch 36 is disposed betweenthe charge pump circuit 12 and the switch circuit 14, in a similarconfiguration to those discussed previously. As depicted, the chargepump circuit 12 is capable of providing a voltage output (Vbb) that hasa voltage level below the common voltage (Vcc) or negative voltagelevel. For example, in the illustrated embodiment, a voltage level ofzero volts (0V) is provided to the charge pump circuit 12 via an inputnode 75, and a low (e.g., a negative) voltage output (Vbb) of the chargepump circuit 12 is output via the path 16. As depicted, the charge pumpcircuit 12 includes a plurality of transistors 76 and capacitors 77having a configuration that is similar to that discussed previously withregard to FIG. 1. The switch circuit 14 includes a first pair oftransistors 78 a, a second pair of transistors 78 b, and an inverter 79.A switch control signal (SW) is input to the switch circuit 14 tocontrol whether the switch circuit 14 is enabled or disabled. In oneembodiment, the switch control signal (SW) may alternate betweenapproximately 0V and the common voltage (Vcc) to control the state ofthe switching circuit 14. In the illustrated embodiment, the switchcontrol signal (SW) is input at a terminal of a first of the second pairof transistors 78 b, and the switch control signal (SW) is routed to agate of a second of the second pair of transistor 78 b after passingthrough the inverter 79. Further, the common voltage (Vcc) is coupled toone of a source and a drain node of the second pair of transistors 78 b,and an input voltage (Vbbo) is coupled to one of a source node and adrain node of the first pair of transistors 78 a. The output voltage(Vout) of the switch circuit 14 is output via the path 18, as discussedpreviously with regard to FIG. 1. Accordingly, in operation of thevoltage generator 10, the output (Vbb) of the charge pump circuit 12 canbe routed via the cut-off switch 36 the switch and the switch circuit 14based on the control signals (disableb and SW). It should be noted thatother embodiments may include any combination of the previouslydiscussed embodiments. For example, the embodiment depicted in FIG. 11may be modified to include the discharging circuits discussed withregard to FIGS. 5-10.

The previous embodiments have been discussed with regard to a voltagegenerator 10. As will be appreciated voltage generators 10 can beincluded in any variety of electronic devices and processor basedsystems. For example, FIG. 12 illustrates a block diagram depicting aprocessor-based system, generally designated by reference numeral 80.The system 80 may be any of a variety of types such as a computer,pager, cellular phone, personal organizer, control circuit, etc. In atypical processor-based device, a processor 82, such as amicroprocessor, controls the processing of system functions and requestsin the system 80. Further, the processor 82 may comprise a plurality ofprocessors that share system control.

The system 80 typically includes a power supply 84. For instance, if thesystem 80 is a portable system, the power supply 84 may advantageouslyinclude permanent batteries, replaceable batteries, and/or rechargeablebatteries. The power supply 84 may also include an AC adapter, so thesystem 80 may be plugged into a wall outlet, for instance. The powersupply 84 may also include a DC adapter such that the system 80 may beplugged into a vehicle cigarette lighter, for instance.

Various other devices may be coupled to the processor 82 depending onthe functions that the system 80 performs. For instance, a userinterface 86 may be coupled to the processor 82. The user interface 86may include buttons, switches, a keyboard, a light pen, a mouse, and/ora voice recognition system, for instance. A display 88 may also becoupled to the processor 82. The display 88 may include an LCD display,a CRT, LEDs, and/or an audio display, for example.

Furthermore, an RF sub-system/baseband processor 90 may also be coupleto the processor 82. The RF sub-system/baseband processor 90 may includean antenna that is coupled to an RF receiver and to an RF transmitter(not shown). A communications port 92 may also be coupled to theprocessor 82. The communications port 92 may be adapted to be coupled toone or more peripheral devices 94 such as a modem, a printer, acomputer, or to a network, such as a local area network, remote areanetwork, intranet, or the Internet, for instance.

Because the processor 82 controls the functioning of the system 80 byimplementing software programs, memory is used to enable the processor82 to be efficient. Generally, the memory is coupled to the processor 82to store and facilitate execution of various programs. For instance, theprocessor 82 may be coupled to system memory 96, which may includevolatile memory, such as Dynamic Random Access Memory (DRAM) and/orStatic Random Access Memory (SRAM). The system memory 96 may alsoinclude non-volatile memory, such as read-only memory (ROM), EEPROM,and/or flash memory to be used in conjunction with the volatile memory.As discussed further below, the system memory 96 may include one or morememory devices, such as flash memory devices, that may include afloating gate memory array fabricated in accordance with one or moreembodiments of the present invention.

FIG. 13 is a block diagram illustrating a flash memory device 98 thatmay be included as a portion of the system memory 96 of FIG. 1. As willbe described further below with respect to FIG. 14, the flash memorydevice 98 may be a NAND flash memory device. The flash memory device 98generally includes a memory array 100. The memory array 100 generallyincludes many rows and columns of conductive traces arranged in a gridpattern to form a number of memory cells. The rows or “row lines” thatmake up the memory array 100 are generally referred to as “wordlines.”The columns or “column lines” are generally referred to as “bit lines”or “digit lines.” The size of the memory array 100 (i.e., the number ofmemory cells) will vary depending on the size of the flash memory device98.

To access the memory array 100, a row decoder block 102 and a columndecoder block 104 are provided and are configured to receive andtranslate address information from the processor 82 via the address bus106 and the address buffer 108 to access a particular memory cell in thememory array 100. A sense amplifier block 110 having a plurality of thesense amplifies is also provided inline with the column decoder 104 andthe memory array 100 to sense and amplify individual values stored inthe memory cells. A row driver block 114 is provided to activate aselected word line in the memory array according to a given row address.

An internal voltage source 112, such as a voltage generator, is providedto deliver voltages for use within the memory device 98. For instance,the internal voltage source 112 may provide voltage levels for program,read and erase operations.

During read and program operations, data may be transferred to and fromthe flash memory device 98 via the data bus 116. The coordination of thedata and address information may be conducted through a control circuit118. Further, the control circuit 118 may be configured to receivecontrol signals from the processor 82 via the control bus 120. A commandbuffer 122 may be configured to temporarily store commands of thecontrol circuit 118. The control circuit 118 is coupled to each of therow decoder block 102, the column decoder block 104, the address buffer108, the sense amplifier block 110, the internal voltage generator 112,the row driver block 114, and the command buffer 122, and is generallyconfigured to coordinate timing and control among the various circuitsin the flash memory device 98.

FIG. 14 illustrates an embodiment of the memory array 100, of FIG. 2. Inthe present embodiment, the memory array 100 comprises a NAND memoryarray 124. The NAND memory array 124 includes word lines WL(0)-WL(M) andintersecting local bit lines BL(0)-BL(N). As will be appreciated, forease of addressing in the digital environment, the number of word linesWL and the number of bit lines BL are each a power of two (e.g., 256word lines WL by 4,096 bit lines BL). The local bit lines BL are coupledto global bit lines (not shown) in a many-to-one relationship.

The NAND memory array 124 includes a floating gate transistor 126located at each intersection of a word line WL and a local bit line BL.The floating gate transistors 126 serve as non-volatile memory cells forstorage of data in the NAND memory array 124, as previously described.As will be appreciated, each floating gate transistor includes a source,a drain, a floating gate, and a control gate. The control gate of eachfloating gate transistor 126 is coupled to a respective word line WL.The floating gate transistors 126 are connected in series, source todrain, to form a NAND string 128 formed between gate select lines.Specifically, the NAND strings 128 are formed between the drain selectline GS(D) and the source select line GS(S). The drain select line GS(D)is coupled to each NAND string 128 through a respective drain selectgate 130. Similarly, the source select line GS(S) is coupled to eachNAND string 128 through a respective source select gate 132. The drainselect gates 130 and the source select gates 132 may each comprise afield-effect transistor (FET), for instance. A column of the memoryarray 124 includes a NAND string 128 and the source select gate 132 anddrain select gate 130 connected thereto. A row of the floating gatetransistors 126 are those transistors commonly coupled to a given wordline WL.

The source of each source select gate 132 is connected to a commonsource line CSL. The drain of each source select gate 132 is coupled tothe source of a floating gate transistor 126 in a respective NAND string128. The gate of each source select gate 132 is coupled to the sourceselect line GS(S).

The drain of each drain select gate 130 is connected to a respectivelocal bit line BL for the corresponding NAND string 128. The source ofeach drain select gate 130 is connected to the drain of a floating gatetransistor 126 of a respective NAND string 128. Accordingly, asillustrated in FIG. 3, each NAND sting 128 is coupled between arespective drain select gate 130 and source select gate 132. The gate ofeach drain select gate 130 is coupled to the drain select line GS(D).

During operation of the NAND memory array 124, various voltages aregenerated within the memory device 98. For instance, the memory devicemay require multiple voltage levels applied to the word lines, bitlines, and the like, to program, read, erase and verify values stored inthe cells of the memory array 100. Accordingly, the voltage generator112 of FIG. 13 may be representative of one or multiple internal voltagegenerators (such as the voltage generator 10) that each output aspecific voltage. During operation, each internal voltage generator 112may receive and condition an externally supplied voltage, e.g., commonbus voltage, and output a voltage level (i.e., “output voltage”) desiredfor the various operations within the memory device 98. It is generallydesired that each output voltage include an accurate voltage level sothat each memory operation, i.e., program, read, erase and verify, isconducted properly. The voltage generator 112 may include anycombination of the embodiments discussed previously with regard to FIGS.1-11.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and will be described in detail herein. However,it should be understood that the invention is not intended to be limitedto the particular forms disclosed. Rather, the invention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the invention as defined by the following appended claims.

What is claimed is:
 1. A device for generating voltage, comprising: acharge pump circuit comprising a first transistor; a high-voltage switchcircuit coupled to a cut-off switch circuit; the cut-off switch circuitconfigured to be enabled when the charge pump circuit is operating anddisabled when the charge pump circuit is not operating to reduce leakagecurrent from the charge pump circuit, the cut-off switch comprising asecond transistor, wherein an output of the charge pump circuit iscoupled to one of a source node and a drain node of the secondtransistor, and a first control signal is input at a gate of the secondtransistor; and a discharge circuit configured to discharge the chargepump circuit to a lower potential when the charge pump circuit is notoperating.
 2. The device of claim 1, wherein the first transistor is ofa first conductivity type and the second transistor is of a secondconductivity type that is different from the first conductivity type. 3.The device of claim 1, wherein the second transistor is a pmosfetdevice.
 4. The device of claim 1, wherein the charge pump circuit isconfigured to receive a supply voltage, and wherein a voltage level of alogic-high of the first control signal is the same as a level of thesupply voltage.
 5. The device of claim 1, wherein the first controlsignal is logic-high during a period when the charge pump circuit is notoperating.
 6. The device of claim 1, wherein the charge pump circuit isconfigured to output a negative voltage.
 7. The device of claim 1,wherein the first control signal is logic-low during a period when thecharge pump circuit is not operating.
 8. The device of claim 1, whereinthe high-voltage switch circuit is configured to route voltage output bythe charge pump circuit to various locations in a memory device.
 9. Thedevice of claim 8, wherein the various locations comprise a gate of amemory cell in the memory device.
 10. The device of claim 1, wherein thedischarge circuit is coupled to one of the source node and the drainnode of the second transistor.
 11. The device of claim 10, wherein thedischarge circuit comprises a third transistor, wherein one of sourcenode and the drain node of the second transistor is coupled to one of asource node and a drain node of the third transistor, and a secondcontrol signal is input at a gate of the third transistor.
 12. Thedevice of claim 11, wherein the first control signal and the secondcontrol signal are the same.
 13. The device of claim 11, wherein a stateof the first control signal is configured to change from a first stateto a second state after the second control signal changes from the firststate to the second state, and the first control signal is configured tochange from the second state to the first state prior to the secondcontrol signal changing from the second state to the first state. 14.The device of claim 10, wherein the discharge circuit comprises a thirdtransistor and a fourth transistor, wherein one of the source node andthe drain node of the second transistor is coupled to one of a sourcenode and a drain node of the third transistor, one of a source node anda drain node of the third transistor is coupled to one of a source nodeand a drain node of the fourth transistor, and a second control signalis input at a gate of the third transistor, and a third control signalcomprising the inverse of the second control signal is input at a gateof the fourth transistor.
 15. The device of claim 14, wherein the thirdtransistor comprises a depletion type nmosfet device and the fourthtransistor comprises an enhancement type pmosfet device.
 16. The deviceof claim 1, wherein the charge pump circuit comprises a thirdtransistor, a first capacitor, and a second capacitor; wherein thedischarge circuit comprises: a fourth transistor coupled to a gate ofthe first transistor, wherein the fourth transistor is configured todischarge the gate of the first transistor to a lower potential when thecharge pump circuit is not operating; a fifth transistor coupled to agate of the third transistor, wherein the fifth transistor is configuredto discharge the gate of the third transistor to a lower potential whenthe charge pump circuit is not operating; a sixth transistor coupled tothe first capacitor, wherein the sixth transistor is configured todischarge the first capacitor to a lower potential when the charge pumpcircuit is not operating; a seventh transistor coupled to the firstcapacitor, wherein the sixth transistor is configured to discharge thefirst capacitor to a lower potential when the charge pump circuit is notoperating; and an eighth transistor, coupled to the fourth, fifth,sixth, and seventh transistors.
 17. A method for generating voltage,comprising: enabling a first transistor coupled to an output of a chargepump circuit when the charge pump circuit is operating; disabling thefirst transistor coupled to the output of the charge pump circuit whenthe charge pump circuit is not operating; and enabling a secondtransistor coupled to the first transistor to discharge the charge pumpcircuit to a lower potential when the charge pump circuit is notoperating.
 18. The method of claim 17, wherein disabling the firsttransistor comprises reducing current across the transistor to reduce astand-by leakage current from the charge pump circuit.
 19. The method ofclaim 17, comprising disabling a second transistor coupled to one of asource node and a drain node of the first transistor when the chargepump circuit is operating.
 20. The method of claim 19, wherein enablingand disabling the first transistor and the second transistor comprisesinputting a first control signal to the first transistor and a secondcontrol signal to the second transistor, wherein the first controlsignal and the second control signal are the same.
 21. The method ofclaim 19, wherein enabling and disabling the first transistor and thesecond transistor comprises inputting a first control signal to thefirst transistor and a second control signal to the second transistor,and wherein the first control signal is configured to transition from afirst state to a second after the second control signal transitions fromthe first state to the second state, and to transition from the secondstate to the first prior to the second control signal transitioning fromthe second state to the first state.
 22. A circuit for generatingvoltage, comprising: a charge pump circuit comprising a firsttransistor; a high-voltage switch circuit coupled to a cut-off switchcircuit; the cut-off switch arranged to be enabled or disabled based onan operation of the charge pump circuit to reduce leakage current fromthe charge pump circuit, the cut-off switch comprising a secondtransistor, wherein an output of the charge pump circuit is coupled toone of a source node and a drain node of the second transistor, and afirst control signal is input at a gate of the second transistor; and adischarge circuit coupled to one of the source node and the drain nodeof the second transistor, wherein the discharge circuit comprises athird transistor and a fourth transistor, wherein one of the source nodeand the drain node of the second transistor is coupled to one of asource node and a drain node of the third transistor, one of a sourcenode and a drain node of the third transistor is coupled to one of asource node and a drain node of the fourth transistor, and a secondcontrol signal is input at a gate of the third transistor, and a thirdcontrol signal comprising the inverse of the second control signal isinput at a gate of the fourth transistor.
 23. A device, comprising: acharge pump circuit comprising: an internal node at a gate of a firsttransistor or a first capacitor in the charge pump circuit, wherein thefirst transistor and the first capacitor are configured to enable thecharge pump circuit to generate a high voltage; and an output node on anoutput path of the charge pump circuit, wherein the output path isconfigured to output the high voltage from the charge pump circuit; afirst discharge circuit coupled to the internal node of the charge pumpcircuit, wherein the first discharge circuit is configured to dischargethe internal node to a lower potential during a period when the chargepump circuit is not operating; and a second discharge circuit coupled tothe output node of the charge pump circuit, wherein the second dischargecircuit is configured to discharge the output node to a lower potentialduring the period when the charge pump circuit is not operating.
 24. Thedevice of claim 23, comprising a third discharge circuit coupled to agate of the first transistor, wherein the third discharge circuit isconfigured to discharge the gate of the first transistor to a lowerpotential during the period when the charge pump circuit is notoperating, wherein the first discharge circuit is coupled to the firstcapacitor.
 25. The device of claim 24, wherein the charge pump circuitcomprises a second transistor and a second capacitor configured toenable the charge pump circuit to generate the high voltage; wherein thedevice comprises: a fourth discharge circuit coupled to a gate of thesecond transistor, wherein the fourth discharge circuit is configured todischarge the gate of the second transistor to a lower potential duringthe period when the charge pump circuit is not operating; and a fifthdischarge circuit coupled to the second capacitor, wherein the fifthdischarge circuit is configured to discharge the second capacitor to alower potential during the period when the charge pump circuit is notoperating.
 26. A voltage generator, comprising: a charge pump circuit; acut-off switch circuit comprising a first transistor, wherein the firsttransistor is configured to be enabled when the charge pump circuit isoperating and disabled when the charge pump circuit is not operating toreduce leakage current from the charge pump circuit; a discharge circuitcoupled to one of a source node and a drain node of the firsttransistor, wherein the discharge circuit is configured to discharge thecharge pump circuit to a lower potential when the charge pump circuit isnot operating; and a high-voltage switch coupled to one of the sourcenode and the drain node of the first transistor.
 27. The voltagegenerator of claim 26, wherein the high-voltage switch is configured toroute voltage output by the charge pump circuit to various locations ina memory device.
 28. The voltage generator of claim 26, wherein thedischarge circuit comprises a second transistor and a third transistor,wherein one of a source node and a drain node of the first transistor iscoupled to one of a source node and a drain node of the secondtransistor, one of a source node and a drain node of the secondtransistor is coupled to one of a source node and a drain node of thethird transistor, and a first control signal is input at a gate of thesecond transistor, and a second control signal comprising the inverse ofthe first control signal is input at a gate of the fourth transistor.